1. Field of the Invention
The present invention relates to a wireless communication apparatus with a transmission power controller and method thereof, and in particular to a wireless communication apparatus and method capable of effectively reducing power to be consumed at transmission time.
2. Description of the Related Art
In a Code Division Multiple Access (CDMA) communication device, transmission power at a mobile station has to be controlled at 70 dB to provide a signal received at a base station at a predetermined power level, for solving the problem of mobile stations being at different distances to the base station or the like. Further, an amplifier is also required to operate in its linear region because the leakage power to adjacent channels cannot be neglected. Thus, the CDMA communication device is required to use a linear compensation circuit for allowing an amplifier to operate in the nonlinear region when high transmission power is required.
In a Personal Digital Cellular (PDC) system, which is the Japanese personal cellular phone standard system, transmission power control on the order of 20 dB is generally performed. In this power control, an amplifier is allowed to operate in the nonlinear operation region. In other words, for a small range of transmission output power control from a PDC or the like, an amplifier is controlled by changing a bias so as to operate at a bias point that provides the least distortion and best efficiency. By controlling the amplifier in this manner, electric current flowing during the idle operation (idle electric current) is minimized.
In this case, the transmission power characteristics of a PDC are as shown in FIG. 1. Namely, when the bias point changes from curve (a) to (d) in FIG. 1, transmission output power Pout changes from the maximum transmission output power (MAX Power) to a range of xe2x88x9215 to xe2x88x9220 dB relative to input power Pin as shown in FIG. 1. At this time, consumed current I also changes from curve (a)xe2x80x2 to (d)xe2x80x2 in FIG. 1 depending on this change in the bias point. In this changing consumed current I graph, the hatched portion in FIG. 1 is an idle current region. In consideration of the stability of an amplifier to suppress oscillation or the like, as shown in FIG. 1, the idle current can be reduced by the power control on the order of 15 dB.
When a linear compensation circuit is provided to carry out linear compensation at all times in a CDMA communication device, the consumed power increases by an amount corresponding to the linear compensation circuit. However, since some wireless communication devices such as mobile communication devices employ a battery as the electric source, it is desirable to reduce its consumed power as much as possible, thus leading to the longest possible duration of device operation. Thus, using a linear compensation circuit has the disadvantage of increasing consumed power and leads to a shortened duration of device operation.
The present invention solves these disadvantages of the related background art, and its object is to provide a consumed-power reduction circuit which is capable of effectively reducing the consumed power during transmission, as well as providing a wireless communication device and a linear operation control method using the same.
It is therefore an object of the present invention to provide a wireless communication apparatus and method capable of effectively reducing consumed power.
Another object of the present invention is to provide a wireless communication apparatus and method capable of effectively controlling linear compensation during non-linear operation of an amplifier.
In order to achieve the above objects, a wireless communication apparatus according to the present invention comprises an amplifier having a linear operation region and a nonlinear operation region, a linear compensation circuit for compensating said amplifier for linearity, and a control circuit for controlling said linear compensation circuit based on a control signal from a base station so as to substantially stop the linear compensation operation of said linear compensation circuit when said amplifier operates in the linear operation region of said amplifier.
In order to achieve the above objects, a method, according to the present invention, of reducing power to be consumed in a wireless communication apparatus having an amplifier with a linear operation region and a nonlinear operation region, and a linear compensation circuit for compensating for linearity of an amplifying operation in the nonlinear operation region of the amplifier, wherein the method includes detecting transmission power of the wireless communication apparatus, and substantially stopping operation of the linear compensation circuit when the transmission power is lower than a predetermined level determined by a control signal from a base station.
To further achieve the objects of the invention, another wireless communication apparatus according to the present invention is provided that comprises an amplifier for performing an amplifying operation in one of either a linear operation region and a nonlinear operation region according to transmission power of the wireless communication apparatus, a linear compensation circuit for compensating the amplifying operation for linearity when in the nonlinear operation region of the amplifier, and a control circuit for controlling operation of the linear compensation circuit when the transmission power is lower than a predetermined level determined by a control signal from a base station.
To still further achieve the objects of the invention, another method according to the present invention is provided, of reducing power to be consumed in a wireless communication apparatus having an amplifier with a linear operation region and a nonlinear operation region and a linear compensation circuit for compensating an amplifying operation of the amplifier for linearity, the method comprises detecting transmission power of the wireless communication apparatus and controlling the linear compensation circuit so as to stop a linear compensation operation of the linear compensation circuit when the transmission power is lower than a predetermined first level determined by a control signal from a base station and to activate the linear compensation operation of the linear compensation circuit when the transmission power exceeds a predetermined second level which is determined by a control signal from a base station and is larger than the predetermined first level.